Hard ferrites are known materials for permanent magnets composed of oxides. Ferrite magnetic materials composed of hard ferrites are provided as permanent magnets in the forms of ferrite sintered bodies and bond magnets. According to the recent miniaturization and advances in electronic components, a need is increasing for permanent magnets composed of ferrite magnetic materials which are miniaturized as well as have high magnetic properties.
Magnetic properties of permanent magnets are generally indicated by a residual magnetic flux density (Br) and a coercive force (HcJ), with high in those values being evaluated as high magnetic properties. In order to improve Br and HcJ of permanent magnets, various compositions of ferrite magnetic materials have been conventionally examined by adding certain elements to the magnetic materials.
In addition to have high Br and HcJ, permanent magnets are preferred to have a high ratio of a value of magnetic field when magnetization is 90% of Br (Hk) to HcJ (Hk/HcJ), so-called a squareness ratio. When Hk/HcJ is high, demagnetization due to external magnetic fields and temperature change can be decreased, and stable magnetic properties can be obtained.
In order to increase Hk/HcJ, the following Patent Literature 1 discloses a method for production of ferrite sintered magnets, wherein particles containing hexagonal ferrite as a main phase are ground to obtain powder for molding, which is a raw material for magnets, having a certain specific surface area at a certain grinding efficiency.